Memory and Identity

In the 1930s the Canadian neurosurgeon Wilder Penfield performed an operation on a patient who had uncontrollable epilepsy.

In the course of the operation, during which the patient was conscious, he electrically stimulated the surface of the patient’s brain. To his surprise the patient had what he called a memory “flashback,” a fragmentary recollection of a childhood event, a scene of himself running home after school. This remarkable demonstration suggested to Penfield that entire scenes from our past are stored in our brains like video tapes. We not only cannot escape our past, but we are, in some very deep sense that past; for whether we are aware of it or not, much of our past is recorded in our brains and it must, in some as yet unknown ways, determine how we behave and what we are. If Penfield’s discovery suggested to many that we were beginning to uncover the roots of our personalities, our identities, they were eventually to be disillusioned. In the 1970s it became evident that Penfield’s “flashbacks” were not memories at all. The nature of memory—and its relation to who we are, our identity—remained as mysterious as ever. Careful study showed that Penfield had performed similar operations more than one thousand times and that the results were not quite as spectacular as he had hoped. In some ninety percent of his operations the patients failed to have memory flashbacks. He was convinced, however, that he had elicited veridical memories in the ten percent of patients who did have memory flashbacks.

But in the 1970s it was discovered that patients only had “flashbacks” when electrical stimulation of the surface of the brain also affected the limbic system, the part of the brain believed to be essential for emotions. Conscious recollection apparently is not possible without some kind of emotional component. It was furthermore shown that the patients were not recalling events from their childhoods, as Penfield had believed, but were constructing recollections out of observations that they had made on their way to the operating rooms. The patients, however, were convinced that their “flashbacks” were real memories. ¹

Penfield’s erroneous interpretation of his patients’ flashbacks had a long and honorable tradition behind it. For ever since neurology became a science in the late nineteenth century it was believed that the brain stored memories in carefully arranged files. Brain damage, it had been believed, destroyed specific files, or bits and pieces of them. Patients with damage to the language center were unable to say or understand specific words, a difficulty that was attributed to the destruction of the “memory images” of those particular words. The idea that a patient could lose the use of specific words and yet be unaffected in his general understanding of the language, was a rather odd argument: for a patient who could no longer use words for colors must have had a very different idea of the nature of the world than those of us who have no difficulty naming colors. Nineteenth-century neurologists were untroubled by such issues. They took it for granted that memories are associated with other memories in what they called the “association cortex.” Colors are associated with objects; if you lose the words for colors this would not change your understanding of the nature of the objects, any more than your loss of the word “knife” would alter your understanding of “meat.” It is difficult to understand what these neurologists thought a patient who could not name colors, but who could see them, understood by sentences such as “You can see the summer has ended because the trees have become yellow,” when the patient had no idea of what “yellow” meant or how it related to the names of other colors. So too, a patient who could not understand the word “knife” must have had a very odd understanding of the sentence “I cut this piece of meat for you.” The relations between “knife” and “to cut,” or “trees” and “colors” are considerably more complex than the idea of an “association memory” implies.

But the neurological evidence appeared to confirm the apparently...